Learn Hardcore Japanese: nihongo de kaiwa no rensyuu wo suru to, nihongo ga dondon zyouzu ni narimasu. - If you practice conversation in Japanese, your Japanese will quickly get better and better.

In English we say “speak in Japanese” or “practice in Japanese,” but Japanese treats this “in” as the same kind of thing as “with a pen” or “by bus” and uses で:

ペンで書く – to write with a pen
バスで行く – to go by bus
日本語で話す – to speak in Japanese

Why not を?

を would mark 日本語 as a direct object:
- 日本語を勉強する – to study Japanese
  Here the action is done to Japanese (you study it), but in your sentence, you are not practicing Japanese itself; you are practicing conversation, and you are doing that practice in Japanese.

Why not に?

に often marks a target/destination or time:
- 学校に行く – go to school
- ３時に会う – meet at 3 o’clock
  It doesn’t fit the idea of “using Japanese as the medium” as well as で does.

What exactly is the function of の in 会話の練習?

The pattern Noun + の + Noun often means “NOUN1’s NOUN2” or “NOUN2 related to NOUN1”.

会話 (conversation)
練習 (practice)
会話の練習 = “practice of conversation” / “conversation practice”

So 会話の練習 is a single noun phrase:
> the practice (練習) that is about conversation (会話)

This pattern is extremely common:

文法の勉強 – study of grammar / grammar study
ピアノの練習 – practice of piano / piano practice
日本語の先生 – teacher of Japanese / Japanese teacher

So 会話の練習をする literally is “to do practice-of-conversation.”

Can I also say 日本語で会話を練習すると instead of 日本語で会話の練習をすると?

Yes, 日本語で会話を練習すると is grammatically correct and understandable.

会話の練習をする
= literally “do practice of conversation” (noun phrase + をする)
会話を練習する
= “practice conversation” (会話 is the direct object of 練習する)

Both are fine, but:

X の練習をする is a very common, natural pattern for “practice X” and might sound a bit more textbook/standard.
X を練習する is also correct but is less frequent in everyday speech in some combinations.

So you’ll see and hear 会話の練習をする more often, but your alternative is not wrong.

Why do we say 練習をする instead of just 練習する? Is there any difference?

Both are possible:

練習をする
練習する

In modern Japanese, many “noun + する” expressions can drop the を without changing the meaning much.

勉強をする → 勉強する
料理をする → 料理する
練習をする → 練習する

Nuance:

練習する is slightly shorter and more colloquial-sounding.
練習をする can sound a bit more careful or slightly formal, but the difference is small.

In your sentence, 会話の練習をすると and 会話の練習すると are both acceptable, though the version with を is a bit more “textbook neat.”

What does と mean in …練習をすると、日本語が…? Is it “and”?

Here と is not “and”; it’s a conditional marker meaning something like:

“when” / “if” / “whenever”

So:

日本語で会話の練習をすると、日本語がどんどん上手になります。
When/If you practice conversation in Japanese, your Japanese gets better and better.

This と-conditional often expresses:

a natural result or
what always happens when something is done.

Compare:

雨が降ると、寒くなります。
When it rains, it gets cold.

It’s different from:

〜たら (more general “if/when”)
〜とき (time “when/at the time that”)

Here, と makes it sound like a general truth / predictable result of practicing.

Why is 日本語 marked with が after the comma, not は?

In 日本語がどんどん上手になります, が marks 日本語 as the subject of the verb なる (“to become”).

The basic pattern is:

X が上手になる = X becomes good / skilled.

So:

日本語が上手になる – Japanese (ability) becomes good
ピアノが上手になる – one becomes good at piano

Could we use は here?

日本語はどんどん上手になります。

This is also grammatically fine, but:

が simply states the fact: “Japanese (ability) will become good.”
は adds a topic/contrast nuance:
- “As for your Japanese, it gets better and better (maybe compared to something else).”

In a neutral, explanatory sentence about cause and effect, が is the more straightforward choice.

What does どんどん mean exactly? How is it different from だんだん?

どんどん is an adverb that roughly means:

rapidly, more and more, steadily and noticeably, often with energy or momentum.

In this sentence:

日本語がどんどん上手になります。
= Your Japanese will get better and better (at a good pace).

Nuance:

どんどん implies:
- progress is clear and often quick or energetic.
だんだん also means “gradually,” but:
- だんだん suggests slow, gradual change.

Compare:

日本語がどんどん上手になります。
Your Japanese improves quickly / noticeably.
日本語がだんだん上手になります。
Your Japanese gradually/imperceptibly improves over time.

Both are positive, but どんどん sounds a bit more active and encouraging.

What is the role of に in 上手になります?

The verb なる (“to become”) normally takes に before the new state:

X になる = to become X

So:

先生になる – become a teacher
きれいになる – become pretty/clean
静かになる – become quiet
上手になる – become skillful / become good (at something)

Here, 上手 (じょうず) is a な-adjective, and when you use a な-adjective with なる, you change it to its adverb-like に form:

上手な
- なる → ✕ (not correct)
上手に
- なる → ✓

So:

日本語がどんどん上手になります。
= Your Japanese becomes more and more skillful.

The に is required by the grammar of X になる.

Why can’t we just say 上手なります without に?

Because with なる, the correct pattern is X になる, not X ななる.

上手 is a な-adjective (上手な人 – a skillful person).
With なる, the form is 上手になる, not 上手ななる.

So:

✕ 日本語がどんどん上手なります。
✓ 日本語がどんどん上手になります。

Think of it as a fixed pattern:

Noun / な-adjective + に + なる
- 先生になる – become a teacher
- 有名になる – become famous
- 上手になる – become good/skilled

(For い-adjectives, you don’t add に, you just use the adjective directly:
寒くなる, 高くなる, 速くなる, etc.)

What tense is なります here? Does it mean present or future?

Japanese non-past form (なります) covers both:

present/habitual (“generally happens”)
future (“will happen”)

In this sentence:

日本語で会話の練習をすると、日本語がどんどん上手になります。

It can be understood as:

Habitual/general truth:
- When you practice conversation in Japanese, your Japanese (in general) gets better and better.
Future prediction (in context of advice):
- If you practice, your Japanese will get better and better.

In English we usually translate it with “will” or a general statement, depending on context:

“If you practice, your Japanese will get better and better.”
“Practicing conversation in Japanese makes your Japanese get better and better.”

Is it okay to drop some particles in casual speech? How might this sentence look in a more casual style?

Yes, in casual spoken Japanese, some particles are often dropped when the meaning is clear.

A natural casual version might be:

日本語で会話の練習すると、日本語どんどん上手になるよ。

Changes:

練習をすると → 練習すると
Dropped を (very common with noun + する).
日本語がどんどん → 日本語どんどん
Sometimes が is dropped in speech when the subject is obvious.
なります → なる
Dictionary/plain form instead of polite ます form.
Added よ at the end to sound friendly/encouraging.

In writing or in polite conversation, keep the particles as in the original sentence. Dropping them is mainly for informal spoken Japanese.

Why is 日本語 mentioned twice? Could we omit the second one?

The sentence repeats 日本語:

日本語で会話の練習をすると、日本語がどんどん上手になります。

You can omit the second 日本語 if it’s clear from context:

日本語で会話の練習をすると、どんどん上手になります。

This would usually be understood as:

“If you practice conversation in Japanese, you get better and better (at Japanese).”

Reasons to repeat it:

Clarity – Makes it absolutely clear that it’s specifically your Japanese ability that gets better.
Emphasis – It ties the cause and result together more strongly:
- Practice Japanese → Japanese improves.

Repeating key nouns like this is quite natural in Japanese, especially in explanations and textbook-style sentences.